Oops, I was not accurate in reporting behavior: I now believe that this fails on Windows XP, but may work 
fine on Linux. Below are my results, showing reproducible failure on XP. The most important thing about 
this is: on XP, once the .pyc file is "broken", Python will not overwrite it, and it must be *manually* 
removed. This is bad!

I will append Ubuntu results in a few minutes.

To reproduce the problem, I had to modify the script to include a "sleep", see attached 
showpyreadonlysleep.sh (cygwin bash script).

Here's the results of running showpyreadonlysleep.sh, then manually reproducing the problem with 
"touch/python":

$ ./showpycreadonlysleep.sh
umask = 0022
CYGWIN_NT-5.1 psimanyi_xp 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin
Python 2.6.2
Running python.exe from: /cygdrive/c/Python26/python
-rw-r--r-- 1 psimanyi mkgroup-l-d 10 May 26 12:43 b.py
b
-rwx------+ 1 psimanyi mkgroup-l-d 137 May 26 12:43 b.pyc
b
-r-x------+ 1 psimanyi mkgroup-l-d 137 May 26 12:43 b.pyc
# c:\Documents and Settings\psimanyi\b.pyc has bad mtime
import b # from c:\Documents and Settings\psimanyi\b.py
# can't create c:\Documents and Settings\psimanyi\b.pyc

And now, running manually:


$ touch b.py

psimanyi@psimanyi_xp ~
$ python -v a.py 2>&1 | grep 'b\.py'
# c:\Documents and Settings\psimanyi\b.pyc has bad mtime
import b # from c:\Documents and Settings\psimanyi\b.py
# can't create c:\Documents and Settings\psimanyi\b.pyc

psimanyi@psimanyi_xp ~
$ touch b.py

psimanyi@psimanyi_xp ~
$ python -v a.py 2>&1 | grep 'b\.py'
# c:\Documents and Settings\psimanyi\b.pyc has bad mtime
import b # from c:\Documents and Settings\psimanyi\b.py
# can't create c:\Documents and Settings\psimanyi\b.pyc

Again, this shows that without removing the .pyc manually, the pyc will not be overwritten, and therefore 
program startup will be slow!